I'm not sure how to answer this. Where on the rectangle the -40 i N force applied? There obviously there must be a counterforce of 40 i N acting on the rectangle to hold it in place, but this force could be at various points of the rectangle or distributed say, along the whole side PQ. We need more information.

Also, the unit of force is N (Newtons), not J (Joules) which is a unit of energy.

-Dan